Tuberculosis is an ancient human scourge that continues to be an important public health problem worldwide. It is an ongoing epidemic of staggering proportions. Approximately one in every three people in the world is infected with Mycobacterium tuberculosis, and has a 10% lifetime risk of progressing from infection to clinical disease. Although tuberculosis can be treated, an estimated 2.9 million people died from the disease last year.
There are significant problems with a reliance on drug treatment to control active M. tuberculosis infections. Most of the regions having high infection rates are less developed countries, which suffer from a lack of easily accessible health services, diagnostic facilities and suitable antibiotics against M. tuberculosis. Even where these are available, patient compliance is often poor because of the lengthy regimen required for complete treatment, and multidrug-resistant strains are increasingly common.
Prevention of infection would circumvent the problems of treatment, and so vaccination against tuberculosis is widely performed in endemic regions. Around 100 million people a year are vaccinated with live bacillus Calmette-Guerin (BCG) vaccine. BCG has the great advantage of being inexpensive and easily administered under less than optimal circumstances, with few adverse reactions. Unfortunately, the vaccine is widely variable in its efficacy, providing anywhere from 0 to 80% protection against infection with M. tuberculosis. 
BCG has an interesting history. It is an attenuated strain of M. bovis, a very close relative of M. tuberculosis. The M. bovis strain that became BCG was isolated from a cow in the late 1800""s by a bacteriologist named Nocard, hence it was called Nocard""s bacillus. The attenuation of Nocard""s bacillus took place from 1908 to 1921, over the course of 230 in vitro passages. Thereafter, it was widely grown throughout the world, resulting in additional hundreds and sometime thousands of in vitro passages. Throughout its many years in the laboratory, there has been selection for cross-reaction with the tuberculin skin test, and for decreased side effects. The net results have been a substantially weakened pathogen, which may be ineffective in raising an adequate immune response.
New antituberculosis vaccines are urgently needed for the general population in endemic regions, for HIV-infected individuals, as well as health care professionals likely to be exposed to tubercle bacilli. Recombinant DNA vaccines bearing protective genes from virulent M. tuberculosis are being developed using shuttle plasmids to transfer genetic material from one mycobacterial species to another, for example see U.S. Pat. No. 5,776,465. Tuberculosis vaccine development should be given a high priority in current medical research goals.
Relevant Literature
Mahairas et al. (1996) J Bacteriol 178(5):1274-1282 provides a molecular analysis of genetic differences between Mycobacterium bovis BCG and virulent M. bovis. Subtractive genomic hybridization was used to identify genetic differences between virulent M. bovis and M. tuberculosis and avirulent BCG. U.S. Pat. No. 5,700,683 is directed to these genetic differences.
Cole et al. (1998) Nature 393:537-544 have described the complete genome of M. tuberculosis. To obtain the contiguous genome sequence, a combined approach was used that involved the systematic sequence analysis of selected large-insert clones as well as random small-insert clones from a whole-genome shotgun library. This culminated in a composite sequence of U.S. Pat. No. 4,411,529 base pairs, with a G+C content of 65.6%. 3,924 open reading frames were identified in the genome, accounting for xcx9c91% of the potential coding capacity.
Mycobacterium tuberculosis (M. tb.) genomic sequence is available at several internet sites.
Genetic markers are provided that distinguish between strains of the Mycobacterium tuberculosis complex, particularly between avirulent and virulent strains. Strains of interest include M. bovis, M. bovis BCG strains, M. tuberculosis (M. tb.) isolates, and bacteriophages that infect mycobacteria. The genetic markers are used for assays, e.g. immunoassays, that distinguish between strains, such as to differentiate between BCG immunization and M. tb. infection. The protein products may be produced and used as an immunogen, in drug screening, etc. The markers are useful in constructing genetically modified M. tb. or M. bovis cells having improved vaccine characteristics.